This five-year-old, Sandy Bridge laptop (Vaio VPCEG13) still uses its original battery (a common 5,300 mAh / 11.1 V) and charger. And it works plugged in over 90 % of the time because it is used as desktop replacement.
Over the years, I have checked ACPI's statistics about the battery capacity and these days its (reported) capacity is 42 % of the original; which accounts for a bit more than two hours (it lasted around five hours when it was brand new.)
Code: Select all
$ acpi --details
Battery 0: Unknown, 99%
Battery 0: design capacity 4932 mAh, last full capacity 2082 mAh = 42%Code: Select all
$ upower --dump
Device: /org/freedesktop/UPower/devices/battery_BAT0
native-path: BAT0
vendor: SONY Corp.
model: VGP-BPS26A
serial: 7964
power supply: yes
updated: (101 seconds ago)
has history: yes
has statistics: yes
battery
present: yes
rechargeable: yes
state: fully-charged
warning-level: none
energy: 26,68 Wh
energy-empty: 0 Wh
energy-full: 26,71 Wh
energy-full-design: 63,27 Wh
energy-rate: 1,639 W
voltage: 12,83 V
percentage: 99%
capacity: 42,2159%
technology: lithium-ion
Last weekend, I decided to test the power management action when the battery enters its critical low level, because the one thing worse than a dying battery is a system which does not save the current work before shutting down. To my surprise, the battery lasted over four hours. Yes, four!
The battery discharged properly and after two hours the system informed me that its capacity had reached 10 % and the charging LED started blinking, just as expected. But when the battery reached 8 %, it did not report further discharging, and I kept using the system for about two more hours. In the meantime, the system always showed the message 8% - under 10 minutes. Around the four-hour mark, it did reach 3 % and the system warned me that it would hibernate soon, a couple of minutes later (when it reached the 2 %), it entered (hybrid) hibernation.
The next morning, I retried this and got the same results. This time, I lowered the action-triggering percentages within UPower, so that the battery would actually drain completely and (hopefully) re-calibrate. It would inform me me at 5 %, warn me at 2 % and shut down at 1 %.
After two hours of use, the battery capacity was near its 10 % and the charging LED started blinking. Once again, the battery stopped informing further discharging under 8 %, and I kept using it two more hours. After about four hours of use, the system finally informed me (at 5 %), then warned me (at 2 %) and finally shut down (at 1 %). I could restart the system twice before the battery was finally depleted and the system shut down automatically each time.
I let the battery rest for over eight hours before recharging it.
Today, I hoped that the battery would be recalibrated, but, as you can see in the output of ACPI and UPower, it is not. It still ran for four hours of use though, yet the battery would stop informing further discharging under 8 %, until it did reach its critical percentage.
Some thoughts:
1. Using the laptop plugged in over 90 % of the time is the number one suspect of messing with the battery calibration.
2. Being almost always plugged in may also translate into very few discharge cycles.
3. For the progressive loss of the battery capacity seemed logical, I always charged it when its percentage was (reported as) low (i.e. after 2:30 hours or so).
4. If the battery has not been properly calibrated for a long time, I might have been re-charging it at a high percentage of its actual capacity (say 40 %, or after 2:30 h of its 4 h duration.)
5. For re-charging at high percentages is often recommended for preserving the battery lifespan, I might have unknowingly saved it.
